1. Technical Field
The present invention relates to a differential gear provided with a clutch means for differential limiting.
2. Background Art
As a differential gear of a motor vehicle, there is widely employed a limited slip differential having a differential limiting function making it possible to transmit a sufficient rotating force to the other wheel via a clutch means at a time when only one wheel is going to run idle. The limited slip differential is employed for preventing the rotating force from being unable to be transmitted to the other wheel on the basis of the idle running of the wheel, for example, in the case that one wheel runs on an ice, a snow or a mud, and for preventing a fishtail phenomenon of a vehicle body at a time of turning, a sudden acceleration or the like.
For example, a differential gear 100 shown in FIG. 8 is described in patent documents 1 and 2. The differential gear 100 is provided with a pair of pressure rings 103 arranged within a differential case 101 so as to be movable in a direction of axles 102 and be relatively non-rotatable, a pinion shaft 104 arranged so as to be orthogonal to the axles 102 in a state in which a shaft end is held between the pressure rings 103, a pinion gear 105 rotatably provided in the pinion shaft 104, a pair of side gears 106 respectively arranged in shaft ends of the right and left axles 102 so as to be non-rotatable and engaging with the pinion gear 105 in both sides while holding the pinion gear 105 therebetween, an operating means 108 operating the pressure rings 103 in a such a direction that a clearance 107 between the pressure rings 103 is enlarged in correspondence to an increase of a relative rotating torque between the pinion shaft 104 and the differential case 101 at a time of the differential, and clutch means 109 arranged in both sides in an axle direction of a pair of pressure rings 103 and operated by the pressure ring 103 so as to limit the differential of the right and left axles 102 in accordance with an enlargement of the clearance 107.
As the operating means 108, there have been proposed the operating means 108 having various shapes, however, there is employed, for example, a structure in which a quadrangular cam portion 110 having one diagonal line set in an axle direction is formed in a shaft end of the pinion shaft 104, and an approximately V-shaped cam groove 111 engaging with a cam portion 110 is formed in the pressure ring 103.
Further, in this differential gear 100, since the relative rotating torque is generated between the pinion shaft 104 and the differential case 101, and the clearance 107 between the pressure rings 103 becomes wider by the operating means 108, the clutch means 109 is actuated so as to limit the differential of the right and left wheels. However, the structure is made such that an elastic member 112 such as a disc spring or the like is arranged in an outer side in the axle direction of both the clutch means 109 in such a manner that the clearance 107 of both the pressure ring 103 is restored to the set interval at a normal time, thereby energizing the pressure rings 103 in a direction of coming close to each other via a plurality of clutch plates 113 of the clutch means 109.
However, since the elastic member 112 of the differential gear 100 energizes the pressure rings 103 in the direction of coming close to each other via the clutch plate 113, the clutch means 109 tends to be operated by the operating means 108 in the case of setting the energizing force to be weak, so that the differential limiting state is formed even at a low speed turning time and the differential state is not stabilized. Further, if the energizing force is made stronger, the operating means 108 comes to a differentiable state, however, since the clutch plate 113 is always frictionally pressure contacted by the energizing force of the elastic member 112 so as to be substantially in a differential limiting state, it is impossible to stably secure the differential state at a low speed turning time. In other words, it is impossible to have a small turning circle at the low speed turning time, and there is generated a so-called chattering phenomenon in which the differential limiting state and the differential state are alternately switched. Accordingly, there are problems that a steering performance is lowered, and the differential gear 100 and there peripheral devices thereof are adversely affected by an impact at a time of the chattering.
Accordingly, in the patent document 3 the applicant of the present invention has proposed a differential gear structured such that an energizing means for energizing both pressure rings in a direction of coming close to each other is provided via no clutch plate, whereby the differential state and the differential limiting state are properly switched, and has put it to a practical use.
Patent Document 1: Japanese Examined Patent Publication No. 55-27980
Patent Document 2: Japanese Unexamined Patent Publication No. 58-221049
Patent Document 3: Japanese Unexamined Patent Publication No. 2001-289305